1. Field of the Invention
Generally described, the invention comprises a wireless communication system with an optimized transport protocol.
2. Description of Related Art
The demand for wireless wide area networks has increased dramatically. Unfortunately, the wireless environment remains hostile for TCP/IP-based ("Transmission Control Protocol/Internet Protocol") communications. One problem is that TCP/IP protocol is laden with overhead and is not reliable under adverse wireless coverage conditions. TCP was designed as a protocol to be used on wired networks between devices that are always connected on a network. It is considered "chatty" in that it uses many data packets to carry essential information. Another problem is that most of the TCP/IP based applications are designed for high-speed connections and as a result end up sending too much data. In other words, conventional wired TCP/IP applications are designed for high-speed networks where system overhead is not an issue. In wireless applications, however, these problems result in poor data throughput, high communications costs, unreliable connections and reduced device battery life.
A typical prior art internet TCP/IP model is illustrated in FIG. 1. In the standard prior art TCP/IP model of FIG. 1, IP-based applications use the Winsock (Windows Sockets) API to communicate via TCP/IP over the Internet, Intranets or corporate LANs.
TCP expects both ends of the communications link (Mobile and Server) to remain connected to the network during the entire exchange. It is, therefore, not well suited for mobile applications where there might be, for example, a blackout. Despite this fact, many in the computer industry still believe that TCP/IP is the best choice for all network communications simply because it is widely used for other Internet, Intranet or LAN computer networks.
In a compromise arrangement, some providers have replaced TCP with User Datagram Protocol (UDP), which is a somewhat friendlier form of TCP. Unlike TCP, UDP is connectionless and unacknowledged during operation. In addition, it does not send a handshake and is truly "send and pray" in that UDP neither acknowledges message receipt nor requests re-transmission of lost packets. When TCP is compared to UDP, we note that TCP requires a minimum of three overhead packets simply to set up the call (open socket) while UDP requires none. Accordingly, TCP sends one acknowledgement for every two packets depending on the window size while UDP sends none. In practice, it has been observed that for every packet sent over CDPD ("Cellular Digital Packet Data") one acknowledgment is sent. This is because TCP's acknowledgment timer expires before the window size is reached on slower, wireless networks, even on CDPD, which is a relatively fast network. For high-speed, low latency networks, the window size is usually reached first. For lower speed, relatively high latency networks, the acknowledgment timer expires first, hence, one acknowledgment per packet.
In addition, TCP requires three or more overhead packets to close the socket (disconnect) while UDP requires none. UDP, by itself, is also a non-reliable protocol, which offsets the advantages of its low overhead. In conclusion, neither TCP nor UDP are well suited for networks that operate with limited bandwidth or over communication links that may be disrupted due to noise coverage problems or system noise.
One alternative to using TCP or UDP is to design a network protocol which allows very little overhead to be used in a connectionless manner and still provide feedback to the application to inform it of packet delivery or non-delivery. Ericsson's Mobitex.RTM. network and Motorola's DataTAC.RTM. network are examples of such networks. They have proprietary protocols which are designed to facilitate optimal use of wireless resources. Such networks are probably more common today than networks which are IP-based. The biggest disadvantage of such networks, however, is that standard TCP or UDP applications cannot be used on them because they are not IP-based. The prior art literature does include descriptions with efforts to improve or optimize wireless communications. See, for example, U.S. Pat. No. 5,673,322 which describes an interface between a protected computer or computer network and the World Wide Web (www), using both wireless and wire line connections. The interface comprises a split proxy system that encapsulates TCP/IP transmissions into a script transmission, which is not subject to problems in high latency systems, thereby greatly improving www access, via a wireless modem or other low-bandwidth communication network.
Other U.S. patent disclosures of possible, but less, relevance include: U.S. Pat. Nos. 5,742,668; 5,742,905; and, 5,327,486.
It was in the context of the foregoing environment that the present invention arose.